Illumination system and exposure apparatus and method

ABSTRACT

An exposure apparatus that exposes an image of a pattern of a mask onto a photosensitive substrate with EUV radiation, and includes a radiation source unit and an exposure apparatus body unit. The exposure apparatus body unit includes an optical integrator, a mirror arranged in an optical path between the radiation source unit and the optical integrator, a detector arranged in an optical path of the exposure apparatus body unit, and a controller which is connected to the detector and which controls an inclination of the mirror based on an output from the detector. In addition, the radiation source unit and the exposure apparatus body unit are installed independently.

FIELD OF THE INVENTION

[0001] The present invention relates to an illumination system capableof providing uniform illumination, and more particularly relates to anexposure apparatus incorporating the illumination system, and asemiconductor device manufacturing method using same.

BACKGROUND OF THE INVENTION

[0002] Conventional exposure apparatus for manufacturing semiconductordevices include an illumination system for illuminating a circuitpattern formed on a mask and projecting this pattern through aprojection optical system onto a photosensitive substrate (e.g., awafer) coated with photosensitive material (e.g., photoresist). One typeof projection optical system employs an off-axis field (e.g., an arcuatefield) and projects and transfers only a portion of the mask circuitpattern onto the wafer if the exposure were static. An exemplaryprojection optical system having such a field comprises two reflectingmirrors, a concave mirror and a convex mirror. In such projectionoptical systems, transfer of the entire mask circuit pattern onto thewafer is performed dynamically by simultaneously scanning the mask andwafer in a fixed direction.

[0003] Scanning exposure has the advantage in that a high resolvingpower is obtained with a comparatively high throughput. In scanning-typeexposure apparatus, an illumination system capable of uniformlyilluminating with a fixed numerical aperture (NA) the entire arcuatefield on the mask is highly desirable. Such an illumination system isdisclosed in Japanese Patent Application Kokai No. Sho 60-232552. Withreference to FIG. 1, an illumination system 10, disclosed therein,comprises, along an optical axis A, an ultrahigh-pressure mercury lamp12, an elliptical mirror 14, and an optical integrator 16. Withreference now also to FIG. 2, optical integrator 16 has an incidentsurface 16 i, an exit surface 16 e, and comprises a combination of foursegmented cylindrical lenses 16 a-16 d. Lenses 16 a and 16 d are locatedat the respective ends of optical integrator 16, are oriented in thesame direction, and have a focal length f1.

[0004] Lenses 16 b and 16 c are located between lenses 16 a and 16 d andare each oriented in the same direction, which is substantiallyperpendicular to the orientation of lenses 16 a and 16 d.

[0005] Adjacent optical integrator 16 is a first condenser opticalsystem 18 and a slit plate 20. With reference now also to FIG. 3, thelatter includes an arcuate aperture 20A having a width 20W and a cord20C. Adjacent slit plate 20 is a condenser optical system 22 and a mask24.

[0006] Mercury lamp 12 generates a light beam 26 which is condensed byelliptical mirror 14 onto incident surface 16 i of optical integrator16. By virtue of having two different focal lengths, optical integrator16 causes light beam 26, passing therethrough, to have differentnumerical apertures in orthogonal directions to the beam (e.g., in theplane and out of the plane of the paper, as viewed in FIG. 1). Lightbeam 26 is then condensed by condenser optical system 18 and illuminatesslit plate 20 and arcuate aperture 20A. Light beam 26 then passestherethrough and is incident condenser optical system 22, whichcondenses the light beam to uniformly illuminate a portion of mask 24.

[0007] With continuing reference to FIG. 3, a rectangular-shaped region28 on slit plate 20 is illuminated so that at least arcuate aperture 20Ais irradiated. Thus, light beam 26 is transformed from a rectangularcross-section beam to an arcuate illumination beam, corresponding toaperture 20A. Note that aperture 20A passes only a small part of thebeam incident slit plate 20.

[0008] Generally, arcuate cord 20C is made long to increase the size ofthe exposure field on the wafer. In addition, arcuate slit width 20W isset comparatively narrow to correspond to the corrected region of theprojection optical system used in combination with illumination system10. The illumination efficiency is determined by the ratio of surfacearea of arcuate aperture 20A to rectangular-shaped region 28. This ratiois small for illumination system 10, an indication that the system isvery inefficient, which is disadvantageous. As a result, the amount oflight reaching mask 24 is fixed at a relatively low level. Since thetime of exposure of mask 24 is inversely proportional to the amount oflight (i.e., intensity) at the mask (i.e., the more intense the light,the shorter the exposure time), the scanning speed of the mask islimited. This limits the exposure apparatus' ability to process anincreasingly large number of wafers (e.g., to increase throughput).

SUMMARY OF THE INVENTION

[0009] The present invention relates to an illumination system capableof providing uniform illumination, and more particularly relates to anexposure apparatus incorporating the illumination system, and asemiconductor device manufacturing method using same.

[0010] Accordingly, the present invention has the goals of providing anillumination system capable of supporting higher throughput with anillumination efficiency markedly higher than heretofore obtained.Another goal is to maintain uniform illumination (e.g., uniform Köhlerillumination).

[0011] There has been a strong desire in recent years for anext-generation exposure apparatus capable of projecting and exposing apattern having a much finer line width onto a photosensitive substrateby using a light source, such as a synchrotron, that supplies softX-rays. However, prior art illumination systems are not capable ofefficiently and uniformly illuminating a mask with X-ray wavelengthlight (“X-rays”).

[0012] Consequently, the present invention has the further goal ofsupplying an illumination system and exposure apparatus capable ofefficiently and uniformly illuminating a mask with X-rays, and furtherto provide a method for manufacturing semiconductor devices usingX-rays.

[0013] Accordingly, a first aspect of the invention is an illuminationsystem for illuminating a surface over an illumination field having anarcuate shape. The system comprises a light source for providing a lightbeam and an optical integrator. The optical integrator includes a firstreflective element group having an array of first optical elements eachhaving an arcuate profile corresponding to the arcuate shape of theillumination field. Each first optical element also includes aneccentric reflecting surface comprising an off-axis section of aspherical reflecting surface or an off-axis section of an asphericalreflecting surface. The array of first optical elements is designed soas to form a plurality of arcuate light beams capable of formingmultiple light source images. The illumination system further includes acondenser optical system designed so as to condense the plurality ofarcuate light beams to illuminate the surface over the arcuateillumination field in an overlapping manner.

[0014] A second aspect of the invention is the illumination system asdescribed above, wherein the condenser optical system comprises acondenser mirror with a focal point, with the condenser mirror arrangedsuch that the focal point substantially coincides with the surface to beilluminated.

[0015] A third aspect of the invention is an illumination optical systemas described above, further comprising a second reflective element grouphaving a plurality of second optical elements. Each of the secondoptical elements has a rectangular shape and a predetermined secondreflecting curved surface which is preferably an on-axis section of aspherical or aspherical reflective surface. The first and secondreflecting element groups are opposingly arranged such that the multiplelight source images are formed at the plurality of second opticalelements when the light beam is incident the first reflecting elementgroup.

[0016] A fourth aspect of the invention is an exposure apparatus forexposing the image of a mask onto a photosensitive substrate. Theapparatus comprises the illumination system as described above, a maskstage capable of supporting the mask, and a substrate stage capable ofsupporting the photosensitive substrate. A projection optical system isarranged between the mask stage and the substrate stage, and is designedso as to project a predetermined pattern formed on the mask onto thephotosensitive substrate over an arcuate image field corresponding tothe arcuate illumination field.

[0017] A fifth aspect of the invention is an exposure apparatus asdescribed above, and further including drive apparatus designed so as tosynchronously move the mask stage and the wafer stage relative to theprojection optical system.

[0018] A sixth aspect of the invention is the exposure apparatus asdescribed above, wherein the illumination system includes a firstvariable aperture stop having a first variable diameter. The projectionoptical system further includes a second variable aperture stop having asecond variable diameter. First and second drive systems are operativelyconnected to the first and second variable aperture stops, respectively,so as to change the first and second variable diameters, respectively. Acontrol apparatus is also preferably included. The control apparatus iselectrically connected to the first and second drive units so as tocontrol the coherence factor by varying the first and second variableaperture diameters.

[0019] A seventh aspect of the invention is a method of patterning thesurface of a photosensitive substrate with a pattern on a mask in themanufacturing of a semiconductor device. The method comprising the stepsof first, providing an illumination light beam. The next (i.e., second)step is reflectively dividing the illumination light beam into aplurality of arcuate light beams corresponding to an arcuately shapedillumination field. The next step is condensing the arcuate light beamsonto the mask over the arcuately shaped illumination field. The finalstep is projecting light from the mask onto the photosensitivesubstrate. The present method preferably further includes the steps inthe above-mentioned second step, of first reflecting the light beam froma first array of reflecting elements each having an arcuate shape and areflecting surface having an eccentric curvature, and forming aplurality of light source images, and then second, reflecting light fromthe plurality of light source images with a second array of reflectingelements opposingly arranged relative to the first array of reflectingelements.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020]FIG. 1 is a schematic optical diagram of a prior art illuminationsystem;

[0021]FIG. 2 is a close-up perspective view of the optical integrator ofthe prior art illumination system of FIG. 1;

[0022]FIG. 3 is a top view of the slit aperture of the prior artillumination system of FIG. 1, with the rectangular illumination regionsuperimposed;

[0023]FIG. 4 is a schematic diagram of the exposure apparatus accordingto a first embodiment of the present invention;

[0024]FIG. 5 is a front view of the reflecting element group shown inFIG. 4;

[0025]FIG. 6 depicts the X-Z plane geometry associated with thereflecting elements in the reflecting element group of FIG. 5;

[0026]FIG. 7 depicts the Y-Z plane geometry associated with thereflecting elements in the reflecting element group of FIG. 5;

[0027]FIG. 8 depicts the X-Y plane geometry associated with the arcuateillumination field formed on the mask in the exposure apparatus of FIG.14;

[0028]FIG. 9 is a close-up of the exposure apparatus of FIG. 4 showingthe reflecting action of the reflecting element group;

[0029]FIG. 10 depicts the X-Y plane geometry associated with areflecting element in the reflecting element group of FIG. 5 when thereflecting element is aspherical;

[0030]FIG. 11 depicts the Y-Z plane geometry associated with the arcuateillumination field when the reflecting elements are aspherical;

[0031]FIG. 12 is a close-up view of the condenser optical system of theexposure apparatus of FIG. 4 with an aspherical condenser mirror showingthe reflecting action associated with the creation of secondary lightsources;

[0032]FIG. 13 is a schematic diagram of the exposure apparatus accordingto a second embodiment of the present invention, which includes anoptical integrator having two reflecting element groups;

[0033]FIG. 14 is a front view of the first reflecting element group ofthe exposure apparatus of FIG. 13;

[0034]FIG. 15 is a front view of the second reflecting element group ofthe exposure apparatus of FIG. 13;

[0035]FIG. 16 depicts the geometry in the Y-Z plane associated with thereflecting elements in the first reflecting element group of FIG. 14;

[0036]FIG. 17 depicts the geometry in the X-Z plane associated with thereflecting elements in the first reflecting element group of FIG. 14;

[0037]FIG. 18 depicts the geometry associated with the reflectingelements in the second reflecting element group of FIG. 14;

[0038]FIG. 19 depicts the geometry associated with the reflectingelements in the second reflecting element group of FIG. 14;

[0039]FIG. 20 is a close-up of the exposure apparatus of FIG. 13 showingthe reflecting action of the first and second reflecting element groupsand the condensing action of the condenser optical system;

[0040]FIG. 21 is an alternate embodiment of the exposure apparatus ofFIG. 13, wherein the optical axes of the projection optical system andthe condenser optical system are colinear;

[0041]FIG. 22 is a front view of an alternate embodiment of the firstreflecting element group of the present invention;

[0042]FIG. 23 is a front view of an alternate embodiment of the secondreflecting element group of the present invention;

[0043]FIG. 24 is a perspective schematic illustration of the reflectingaction associated with a single column of the first and secondreflecting element groups shown in FIGS. 22 and 23, respectively;

[0044]FIG. 25 is a first alternate embodiment of the exposure apparatusof FIG. 4, further including a vacuum chamber, a light source unit andvariable aperture stop;

[0045]FIG. 26 is a second alternate embodiment of the exposure apparatusof FIG. 4, further including a turret plate in place of the firstvariable aperture stop, and an adjustable light beam converting unit;

[0046]FIG. 27 is a perspective view of the aperture turret plate of theexposure apparatus of FIG. 26;

[0047]FIG. 28 is a third alternate embodiment of the exposure apparatusof FIG. 4, further including an auxiliary optical integrator;

[0048]FIG. 29 is a front view of the first auxiliary reflecting elementgroup in the auxiliary optical integrator of the exposure apparatus ofFIG. 28;

[0049]FIG. 30 is a front view of the second auxiliary reflecting elementgroup in the auxiliary optical integrator of the exposure apparatus ofFIG. 28;

[0050]FIG. 31 is a fourth alternate embodiment of the exposure apparatusof FIG. 4, wherein the function of the condenser mirror is combined intothe second reflecting element group of the optical integrator; and

[0051]FIG. 32 is a fifth alternate embodiment of the exposure apparatusof FIG. 4, further including a subchamber with a filter for passingX-rays and not dust particles.

DETAILED DESCRIPTION OF THE INVENTION

[0052] The present invention relates to an illumination system capableof providing uniform illumination, and more particularly relates to anexposure apparatus incorporating the illumination system, and asemiconductor device manufacturing method using same.

[0053] With reference to FIGS. 4 and 5, exposure apparatus 50 comprises,along an optical axis A_(c), a light source 54 which supplies light ofwavelength λ<200 nm. A preferred light source is a laser, such as an ArFexcimer laser supplying light of wavelength λ=193 nm, or an F₂ lasersupplying light of wavelength λ=157. Alternatively, light source 54 maybe an X-ray radiating apparatus such as a laser plasma X-ray sourceradiating X-rays of wavelength λ=10-15 nm or λ=5-20 nm, a synchrotrongenerating apparatus radiating light of wavelength λ=10-15 nm, λ=5-20 nmand the like.

[0054] Exposure apparatus 50 further comprises an optical integrator(i.e., a multiple light source forming system) 56. Light beam 100 fromlight source 54 is directed to optical integrator 56. Optical integrator56 is disposed in a predetermined position to receive light beam 100.Optical integrator 56 comprises a reflecting element group 60 having aplurality of reflecting elements E (FIG. 5) arranged two-dimensionallyin dense formation (i.e., in an array) along a predetermined firstreference plane P₁ parallel to the Y-Z plane. Specifically, as shown inFIG. 5, reflecting elements E have reflecting curved surfaces with anarcuate shape (profile). In a preferred embodiment, reflecting elementsE are arranged in a number of columns 62 (e.g., five columns, as shown)arranged along the Y-direction. Each column 62 comprises a plurality ofreflecting elements E arranged along the Z-direction. Furthermore,columns 62 are designed such that together they roughly form a circularshape. The arcuate shape of reflecting elements E is similar to theshape of the arcuate illumination field formed on the mask, as discussedfurther below.

[0055] With reference now to FIGS. 6 and 7, each reflecting element Ecomprises an arcuate section, removed from an optical axis A_(E), of areflecting curved surface S of radius of curvature R_(E). Surface S iscentered on optical axis A_(E) and has an apex O_(E). Further, arcuatereflecting element E has a center C_(E) removed from optical axis A_(E)by a heigh h_(E). Accordingly, each reflecting element E comprises aneccentric reflecting surface RS_(E) which is a section of reflectingcurved surface S. Reflecting surface RS_(E) is the effective reflectingregion of reflecting element E that reflects light (e.g., light beam100) from light source 54.

[0056] With reference again to FIG. 4, exposure apparatus 50 furthercomprises a condenser optical system 64 having a condenser mirror 66removed from optical axis A_(C). Condenser mirror 66 comprises a sectionof a spherical mirror 66′ (dashed line) centered on optical axis A_(C)and having a radius of curvature R_(C) (not shown). Optical axis A_(C)passes through the center of a plane P₂ located on optical axis A_(C).However, the focal point (not shown) of condenser mirror 66 is locatedon optical axis A_(C). The latter is also parallel to each optical axisA_(E) of plurality of optical elements E in optical element group 60.

[0057] Exposure apparatus 50 further comprises a fold mirror 68 forfolding the optical path between condenser optical system 64 and areflective mask M, and a mask stage MS for movably supporting thereflective mask M having a backside M_(B), and a reflective front sideM_(F) with a pattern (not shown), such as a circuit pattern. Mask stageMS is operatively connected to a mask stage drive system 72 for drivingthe mask stage in two-dimensional movement in the X-Y plane. A controlsystem 74 is electrically connected to drive system 72 to control itsoperation.

[0058] A projection optical system 76 is disposed in the optical pathbetween reflective mask M and a photosensitive substrate such as waferW. Projection optical system 76 includes an optical axis A_(P) and ispreferably an off-axis-type reduction system comprising, for example,four aspherical mirrors 78 a-78 d. The latter have effective reflectingsurfaces at positions removed from optical axis A_(P). Mirrors 78 a, 78c and 78 d comprise concave aspherical mirrors, and mirror 78 bcomprises a convex aspherical mirror. A pupil position P is located at areflecting surface S_(C) of mirror 78 c. An aperture stop (not shown) isprovided at pupil position P.

[0059] Exposure apparatus 50 further comprises a wafer stage WS formovably supporting a wafer W having a surface W_(S) coated with aphotosensitive material, such as photoresist. Wafer stage WS isconnected to a wafer stage drive system 92 for driving the wafer stagein two-dimensional movement in the X-Y plane. Drive system 92 is alsoelectrically connected to control system 74 which controls drive system92 and also coordinates the relative driving of drive systems 72 and 92.

[0060] The operation of exposure apparatus 50 is now described withreference to FIGS. 4 and 6. A light beam 100 having a wavefronts 105 anda beam diameter D_(B) emanates from light source 54 and travels parallelto optical axis A_(C) and also parallel to optical axis A_(E) ofreflecting element E (FIG. 6). Light beam 100 then reflects from eachreflecting surface RS_(E) of element E and is condensed at a focal pointposition F_(E) (FIG. 6) on optical axis A_(E). A plurality of lightsource images I are formed corresponding to each reflecting element E(FIG. 6). If focal length f_(E) of reflecting element E is equal to thedistance between apex O_(E) and focal point position F_(E), and R_(E) isthe radius of curvature of the reflecting curved surface S, then therelationship in condition (1) below holds:

f _(E) =−R _(E)/2.  (1)

[0061] With continuing reference to FIGS. 4 and 6, wavefronts 105 oflight beam 100 are incident reflecting element group 60 substantiallyperpendicular, thereby forming, upon reflection from reflecting elementsE, a plurality of converging beams 108 each having an arcuate cross20section (hereinafter, “arcuate light beam”). This results in theformation of plurality of light source images I at plane P₂. Lightsource images I are displaced from incident light beam 100 in directionperpendicular to optical axis A_(E). The number of light source images Icorresponds to the number of reflecting elements E in reflecting elementgroup 60. In other words, assuming light beam 100 is incident reflectingelements E from a direction parallel to each optical axis A_(E), lightsource images I are respectively formed in plane P₂ through which focalpoint position F_(E) passes. In this manner, reflecting element group 60functions as an optical integrator, i.e., a multiple-light-sourceforming optical system capable of forming a plurality of secondary lightsources.

[0062] With continuing reference to FIG. 4, light beams 110 emanatingfrom plurality of light source images I are respectively reflected andcondensed by condenser mirror 66, which forms condensed light beams 116.The latter are deflected by deflection (fold) mirror 68 and arcuatelyilluminate front side M_(F) of mask M in a superimposed manner.

[0063] With reference now to FIG. 8, an arcuate illumination field IF,as formed on mask M when viewed from backside M_(B), has a center ofcurvature O_(IF) on optical axis A_(P) of projection optical system 76.If fold mirror 68 were to be removed, arcuate illumination field IFwould be formed at position (plane) IP, and center of curvature O_(IF)of arcuate illumination field IF would be located on optical axis A_(C).

[0064] In exposure apparatus 50 of FIG. 4, optical axis A_(C) is notdeflected 90° by a fold mirror. However, if optical axis A_(C) were sodeflected by a hypothetical reflecting surface 68A, optical axis A_(C)and optical axis A_(P) would become coaxial and intersect mask M.Consequently, it can be said that optical axes A_(C) and A_(P) areoptically coaxial. Accordingly, condenser mirror 66 and projectionoptical system 76 are arranged such that optical axes A_(C) and A_(P)optically pass through center of curvature O_(IF) of arcuateillumination field IF.

[0065] Light from condensed light beams 116 reflects from front sideM_(F) of mask M, thereby forming a light beam 118 which is incidentprojection optical system 76. The latter forms an image of the patternpresent on mask front side M_(F) over an arcuate image field IF′ onsurface W_(S) of wafer W. Mask stage MS moves two-dimensionally in theX-Y plane via drive system 72, and substrate stage WS movestwo-dimensionally in the X-Y plane via drive system 92. Control system74 controls the drive amount of drive systems 72 and 92. In particular,control system 74 moves mask stage MS and substrate stage WSsynchronously in opposite directions (as indicated by arrows) via thetwo drive systems 72 and 92. This allows for the entire mask pattern tobe scanned and exposed onto surface W_(S) of wafer W through projectionoptical system 76. In this manner, semiconductor devices can bemanufactured, since satisfactory circuit patterns are transferred(“patterned”) onto surface W_(S) of wafer W.

[0066] The operation of reflecting element group 60 is now explained ingreater detail. With reference now to FIG. 9, reflecting element group60 comprises, for the sake of explanation, three reflecting elementsE_(a)-E_(c) arranged along plane P₁ parallel to the Y-Z plane such thatthe position of the center of curvatures (the focal points) of eachreflecting element E_(a)-E_(c) reside on plane P₂.

[0067] Light beam 100 comprises collimated light beams 100 a and 100 ccomprising wavefronts 105 a and 105 c, respectively, that are incidentreflecting elements E_(a) and E_(c). The latter form, from light beams100 a and 100 c, converging arcuate light beams 108 a and 108 c,respectively, which correspond to the profile shape of reflectingsurface RS_(EA) of reflecting element E_(a) and reflecting surfaceRS_(EC) of reflecting element E_(c). Arcuate light beams 108 a and 108 cconverge to form light source images I_(a) and I_(c), respectively, atplane P₂. Subsequently, diverging light beams 110 a and 110 c emanatefrom light source images I_(a) and I_(c) and propagate toward condensermirror 66. The latter condenses light beams 110 a and 110 c, therebyforming condensed light beams 116 a (solid lines) and 116 c (dashedlines). Light beams 116 a and 116 c are condensed by condenser mirror 66such that they overlap (i.e., are super-imposed) and obliquelyilluminate front side M_(F) of mask M over arcuate illumination fieldIF. The Z-direction (i.e., the direction in the plane of the paper)along mask front side M_(F) is the width direction of arcuateillumination field IF.

[0068] Thus, light reflects from each reflecting element E in reflectingelement group 60 and arcuately illuminates mask M over arcuateillumination field IF in an overlapping (i.e., superimposed) manner,allowing uniform illumination to be achieved. Uniform Köhlerillumination is achieved when each light source image I formed by eachreflecting element E is re-imaged at pupil position P of projectionoptical system 76

[0069] Even if the entire illumination system (i.e., elements 54 through68) and projection optical system 76 includes only catoptric members andcatoptric elements, an arcuate illumination field IF with uniformillumination intensity can be efficiently formed on mask M whilesubstantially maintaining Köhler illumination.

[0070] By making the projective relationship of condenser optical system64 a positive projection, mask M can be illuminated with a uniformnumerical aperture (NA), regardless of illumination direction.

[0071] With reference again to FIG. 5, by densely arranging reflectingelements E such that reflecting element group 60 has a roughly circularoutline, the outline (profile) of the secondary light sources formed byplurality of light source images I formed at position P₂ is also roughlycircular. Accordingly, by making the projective relationship ofcondenser mirror 66 a positive projection and by simultaneously settingthe outline (profile) of plurality of light sources I, the spatialcoherence inside arcuate illumination field IF formed on mask M can berendered uniform regardless of the location and direction of incidentbeams 116 (see FIG. 9).

[0072] Furthermore, by configuring the shape of reflecting surfaceRS_(E) of each reflecting element E so that the projective relationshipis identical to that of condenser mirror 66, the illumination intensityin arcuate illumination field IF can be rendered even more uniform,without generating distortion due to reflecting element group 60 andcondenser mirror 66.

[0073] With reference again to FIG. 8, an exemplary arcuate illuminationfield IF has a central arc 130 of radius R_(IF) and an angle α_(IF)=60°,ends IF_(a) and IF_(b) separated by a linear distance L_(IF)=96 mm, awidth W_(IF)=6 mm, and an illumination numerical aperture NA=0.015 atmask M. Further, the inclination of the principle ray (not shown) of theillumination light with respect to the mask normal (not shown) isapproximately 30 mrad (i.e., the entrance pupil position of projectionoptical system 76 is approximately 3119 mm from mask M), and diameterD_(B) of light beam 100 from light source 54 is on the order of 42 mm(FIG. 4).

[0074] The above description considered reflecting elements E andcondenser mirror 66 both with eccentric spherical reflecting surfaces.However, these surfaces can also be aspherical surfaces. Below, specificnumerical values for these surfaces as aspherical surfaces are provided.

[0075] With reference now to FIG. 10, reflecting element E includes anarcuate section, removed from optical axis A_(E), of a reflecting curvedaspherical surface AS_(E) and a reference spherical surface S_(E) havinga common apex O_(E). Spherical surface S_(E) has a center of curvatureO_(RE). The X-axis passes through apex O_(E) in the directionperpendicular to a plane P_(T) tangential at apex O_(E) (optical axisA_(E) of reflecting element E is co-linear with the X-axis). The Y-axispasses through apex O_(E) in the plane of the paper and is perpendicularto the X-axis. The origin of the X-Y coordinate system is apex O_(E).Accordingly, each reflecting element E comprises an eccentric asphericalreflecting surface ARS_(E) which is a section of reflecting curvedaspherical surface AS_(E).

[0076] Aspherical reflecting surface AS_(E) is described by theexpression for an aspherical surface, below, wherein x(y) is thedistance along the direction of the X-axis (optical axis A_(E)) from thetangential plane at apex O_(E) to the surface AS_(E), y is the distancealong the direction of the Y-axis from the X-axis (optical axis A_(E))to reflecting surface AS_(E), R_(E) is the radius of curvature ofreference spherical surface S_(E), and C₂, C₄, C₆, C₈ and C₁₀ areaspherical surface coefficients.

x(y)=(y ² /R _(E))/[1+(1−y ² /R _(E) ²)^(0.5) ]+C ₂ y ² +C ₄ y ⁴ +C ₆ y⁶ +C ₈ y ⁸ +C ₁₀ y ¹⁰

[0077] An exemplary aspherical reflecting surface AS_(E) has thefollowing parameter values:

[0078] R_(E)=−183.3211

[0079] C₂=−5.37852×10⁻⁴

[0080] C₄=−4.67282×10⁻⁸

[0081] C₆=−2.11339×10⁻¹⁰

[0082] C₈=5.71431×10⁻¹²

[0083] C₁₀=−5.18051×10⁻¹⁴

[0084] Each reflecting element E in reflecting element group 60 has areflecting cross-sectional shape that interposes heights y₁ and y₂ fromoptical axis A_(E) and comprises an arcuate aspherical eccentric mirror.In an exemplary illumination system 50 illustrated in FIG. 11, lengthL_(IF) between ends IF_(a) and IF_(b) of arcuate illumination field IFat an arc open angle α_(E) of 60° is approximately 5.25 mm (see FIG.11), height y₁ is approximately 5.085 mm, height y is approximately 5.25mm, and height y₂ is approximately 5.415 mm.

[0085] In this case, plurality of light source images I (FIG. 10) formedby reflecting element E are formed at a position axially removed fromapex O_(E) by X₁=76.56 mm, with height y=5.25 mm from the centerdiameter arc 130 (FIG. 11). The position of light source images I in adirection perpendicular to optical axis A_(E) is removed by y₁=5.085 mmfrom the inner diameter IF_(i) of arcuate illumination field IF, and isremoved by y₂=5.415 mm from the outer diameter IF_(o).

[0086] Thus, a satisfactory reflecting element group 60 (FIG. 5) can beconstituted by arranging, in columns, a plurality of eccentricaspherical reflecting elements E having the above dimensions.

[0087] Next, an exemplary condenser mirror 66 in condenser opticalsystem 64, for the case where reflecting element group 60 comprises aplurality of eccentric aspherical reflecting elements E having the abovedimensions, is discussed.

[0088] With reference now to FIG. 12, condenser mirror 66 comprises, ina preferred embodiment, a section ARS_(C) of reflective an asphericalsurface AS_(C), with associated reference spherical surface S_(C) havinga common apex O_(C). Reference spherical surface S_(C) has a center ofcurvature O_(RC). The X-axis is the direction perpendicular to atangential plane P′_(T) at apex O_(C) (optical axis A_(C) is theX-axis). The Y-axis is the direction parallel to tangential plane P′_(T)at apex O_(C). The origin of the X-Y coordinate system is apex O_(C).

[0089] Reflecting aspherical surface AS_(C) associated with condensermirror 66 is described by the expression for an aspherical surfacebelow, wherein x(y) is the distance along the direction of the X-axis(optical axis A_(C)) from tangential plane P′_(T) at apex O_(C) toreflecting aspherical surface AS_(C), y is the distance along the Y-axisfrom the X-axis (optical axis A_(C)) to reflecting aspherical surfaceAS_(C), R_(C) is the radius of curvature of reference spherical surfaceS_(C), and C₂, C₄, C₆, C₈ and C₁₀ are aspherical surface coefficients.

x(y)=(y ² /R _(C))/[1+(1−y ² /R _(C) ²)^(0.5) ]+C ₂ y ² +C ₄ y ⁴ +C ₆ y⁶ +C ₈ y ⁸ +C ₁₀ y ¹⁰

[0090] Specific numerical values for the present example are as follows:

[0091] R_(C)=−3518.74523

[0092] C₂=−3.64753×10⁻⁵

[0093] C₄=−1.71519×10⁻¹¹

[0094] C₆=1.03873×10⁻¹⁵

[0095] C₈=−3.84891×10⁻²⁰

[0096] C₁₀=5.12369×10⁻²⁵

[0097] With continuing reference to FIG. 12, light source images Iformed by reflecting element group 60 are formed in plane P₂ orthogonalto optical axis A_(C) (see FIG. 4). In the present example, plane P₂ isat a position removed by approximately x_(IC)=2009.8 mm along opticalaxis A_(C) from apex O_(C).

[0098] Arcuate illumination field IF having a uniform illuminationintensity distribution and spatial coherence is formed by condensermirror 66 receiving diverging light beams 110 and forming converginglight beams 116. Arcuate illumination field IF is formed by condensermirror 66 at a position C_(IF) removed by x_(M)=1400 mm from apex O_(C)(or plane P′_(T)) and approximately y_(MC)=96 mm from optical axisA_(C).

[0099] By the abovementioned configuration, an arcuate illuminationfield IF having a uniform illumination intensity and spatial coherencecan be formed on mask M.

[0100] In a preferred embodiment of the present invention, condition (2)below, is satisfied:

0.01<|f _(F) /f _(C)|<0.5  (2)

[0101] wherein f_(F) is the focal length of each reflecting element E inreflective element group 60 and f_(C) is the focal length of condenseroptical system 64 (e.g., the focal length of condenser mirror 66).

[0102] If |f_(F)/f_(C)| exceeds the upper limit in condition (2), thefocal length f_(C) of condenser optical system 64 shortens in theextreme when an appropriate power is given to each reflecting element E.Consequently, it is difficult to form a uniform arcuate illuminationfield IF on mask M, since strong aberrations are generated by condenseroptical system 64. On the other hand, if |f_(F)/f_(C)| falls below thelower limit in condition (2), the focal length f_(C) of condenseroptical system 64 increases excessively, with the result that theelements in the condenser optical system (e.g., condenser mirror 66)increase in size excessively. This makes it difficult to maintain acompact illumination system when the appropriate power is given to eachreflecting element E.

[0103] By way of example, for the case where each reflecting element Ein reflecting element group 60 has radius of curvature R_(E)=−183.3211mm, the reference focal length f_(F)=91.66055 mm (f_(F)=−R_(E)/2). Inaddition, for a corresponding condenser mirror 66 with a radius ofcurvature R_(C)=−3518.74523 mm, reference focal length f_(C)=1759.3726mm (f_(C)=−R_(C)/2). Accordingly,

|f _(F) /f _(C)|=0.052.

[0104] Thus, condition (2) is satisfied and an illumination system canbe compactly constituted while maintaining a satisfactory illuminationregion.

[0105] The above first mode for carrying out the present invention showsan example wherein optical integrator 56 comprises one reflectingelement group 60 (FIG. 4). In a second mode for carrying out the presentinvention, the optical integrator comprises two reflecting elementgroups, as described below.

[0106] With reference now to FIG. 13, illumination system 200 comprisesessentially the same components as illumination optical system 50 ofFIG. 4, except that optical integrator 220, analogous to opticalintegrator 56 in system 50 of FIG. 4, comprises first and secondopposingly arranged reflecting element groups 220 a and 220 b. Firstreflecting element group 220 a is constituted so that a first pluralityof reflecting elements E₁ (not shown in FIG. 13) are densely arranged intwo dimensions along a predetermined reference plane (first referenceplane) P_(a) parallel to the Y-Z plane. Specifically, with reference toFIG. 14, first reflecting element group 220 a includes a plurality ofreflecting elements E₁ each having an arcuate curved reflecting surface,arranged as described above in connection with elements E of reflectingelement group 60.

[0107] With reference now also to FIGS. 16 and 17, each reflectingelement E₁ in first reflecting element group 220 a has an arcuate shape(profile) of one part of a reflecting curved surface S₁ of radius ofcurvature R_(E1) in a region eccentric from optical axis A_(E1). CenterC_(E1) of arcuate reflecting element E₁ is positioned at height h_(E)from optical axis A_(E1). Accordingly, the eccentric reflecting surfaceRS_(E1) of each reflecting element E₁, as shown in FIGS. 16 and 17,comprises an eccentric spherical mirror having a radius of curvatureR_(E1).

[0108] Consequently, with reference to FIG. 17, a portion of light beam100 impinging from an oblique direction with respect to optical axisA_(E1) is condensed to form a light source image I in plane P_(FO) at aposition removed from optical axis A_(E1) in a direction perpendicularto focal point position F_(E1) of reflecting element E₁. Reflectingelement E₁ has a focal length f_(E1), which is the distance between apexO_(E1) and focal point position F_(E1).

[0109] In a preferred embodiment of the present invention, condition(3), below, is satisfied:

f _(E1) =−R _(E1)/2.  (3)

[0110] With reference again to FIG. 15, second reflecting element group220 b comprises a plurality of second reflecting elements E₂ denselyarranged in two dimensions along a predetermined reference plane (secondreference plane) P_(b) parallel to the Y-Z plane. Specifically, secondreflecting element group 220 b includes a plurality of reflectingelements E₂ having reflecting curved surfaces which have a rectangularprofile (outline). Second reflecting element group 220 b has along theY-direction a plurality of columns 262 (e.g., five, as shown), eachcomprising a plurality of second reflecting elements E₂ arranged in arow along the Z-direction. Furthermore, columns 262 of second reflectingelements are arranged to collectively form a near circular shape (i.e.,outline).

[0111] In other words, each of second reflecting elements E₂ in secondreflecting element group 220 b is arranged in a row facing, inone-to-one correspondence, each of first reflecting elements E₁comprising first reflecting element group 220 a.

[0112] With reference now to FIGS. 18 and 19, each reflecting element E₂has a reflecting surface RS_(E2) having a rectangular profile (outline)that is one part of a reflecting curved surface S₂ with a radius ofcurvature R_(E2) in a region including optical axis A_(E2). Accordingly,reflecting element E₂ has a rectangular perimeter 270 and a centerC_(E2) which coincides with optical axis A_(E2). Accordingly, reflectingsurface RS_(E2) of each reflecting element E₂ comprises a concentricspherical mirror with radius of curvature R_(E2).

[0113] With reference again to FIG. 13, wavefronts 105 in beam 100 areincident first reflecting element group 220 a obliquely from apredetermined direction and are split by the first reflecting elementgroup into arcuately shaped segments by the reflecting action ofplurality of reflecting elements E₁. The latter form a plurality oflight source images I (not shown) at plane (second reference plane)P_(b), parallel to the Y-Z plane and displaced from incident light beam100. The number of light source images I corresponds to the number ofreflecting elements E₁. Second reflecting element group 220 b isarranged in plane P_(b).

[0114] Light beam 100 from light source 54, in addition to having aparallel component, also includes a dispersion angle of a certain range.Consequently, each light source image I having a certain size is formedin plane P_(b) by first reflecting element group 220 a. Accordingly,second reflecting element group 220 b functions as a field mirror groupto effectively utilize light supplied from light source 54. In otherwords, each of the plurality of second reflecting elements E₂ in secondreflecting element group 220 b functions as a field mirror.

[0115] With continuing reference to FIG. 13, plurality of light sourceimages I reflected by second reflecting element group 220 b forms aplurality of light beams 310 which are incident condenser mirror 66 witha radius curvature R_(c). The focal point position (not shown) ofcondenser mirror 66 coincides with secondary light source plane P_(b).Center of curvature O_(C) of condenser mirror 66 exists at the centerposition of plurality of light source images I formed on secondreflecting element group 220 b (i.e., the position wherein optical axisA_(C) and plane P_(b) intersect, or the center of reflective elementgroup 220 b).

[0116] Optical axis A_(C) is parallel to each optical axis A_(E1)associated with each reflecting element E₁ in first reflective elementgroup 220 a, but is not parallel to each optical axis A_(E2) associatedwith each reflecting optical element E₂ in second reflective elementgroup 220 b. More particularly, each optical axis A_(E2) associated withreflecting optical elements E₂ is preferably inclined at half the angleof incidence of the obliquely impinging light beam.

[0117] With continuing reference to FIG. 13, light beams 310 fromplurality of light source images I are each reflected and condensed bycondenser mirror 66 thereby forming light beams 316. Light beams 316 arethus made to arcuately illuminate, in a superimposed manner, front sideM_(F) of mask M. Plane mirror 68, as discussed above in connection withapparatus 50 of FIG. 4, may be used as a deflecting mirror to fold theoptical path. With reference again also to FIG. 8, arcuate illuminationfield IF is formed on mask M when viewed from the back side M_(B) ofmask M. Center of curvature O_(IF) of arcuate illumination field IFexists on optical axis A_(P) (FIG. 13). If plane mirror 68 in system 200of FIG. 13 is temporarily eliminated, arcuate illumination field IF isformed at plane IP, and center of curvature O_(IF) of arcuateillumination field IF exists on optical axis A_(C).

[0118] With continuing reference to FIG. 13, optical axis A_(C) ofcondenser optical system 64 is not deflected 90°. However, if opticalaxis A_(C) were deflected 90° by hypothetical reflecting surface 68 a,optical axis A_(C) and optical axis A_(P) would be coaxial on mask M.Consequently, it can be said that optical axes A_(C) and A_(P) areoptically coaxial. Accordingly, as with exposure apparatus 50 of FIG. 4,condenser optical system 64 and projection optical system 76 of exposureapparatus 200 are arranged such that optical axes A_(C) and A_(P)optically pass through center of curvature O_(IF) of arcuateillumination field IF.

[0119] Light beam 118 reflected by front side M_(F) of mask M passesthrough projection optical system 76, as described above, therebyforming an image of the mask pattern on surface W_(S) of wafer W over anarcuate image field IF′ (not shown: see FIG. 4). Wafer surface W_(S) iscoated with photoresist and thus serves as a photosensitive substrateonto which the mask pattern, via the arcuately shaped image of mask M,is projected and transferred.

[0120] As discussed above in connection with exposure apparatus 50 ofFIG. 4, mask stage MS and substrate stage WS move synchronously inopposite directions (as indicated by arrows) via mask stage drive system72 and wafer stage drive system 92. Drive systems 72 and 92 arecontrolled by control system 74 in a manner that allows the entire maskpattern on mask M to be scanned and exposed onto wafer surface W_(S)through projection optical system 76. Consequently, satisfactorysemiconductor devices can be manufactured, since satisfactory circuitpatterns are transferred onto wafer W by a photolithography process thatmanufactures semiconductor devices.

[0121] With reference now to FIG. 20, the operation of first and secondreflecting element groups 220 a and 220 b are described in more detail.For ease of explanation, FIG. 20 omits plane mirror 68. Further, firstreflecting element group 220 a comprises only two reflecting elementsE_(a1) and E_(b1), and second reflecting element group 220 b comprisesonly two reflecting elements E_(a2) and E_(b2).

[0122] Reflecting elements E_(a1) and E_(b1) are arranged along firstreference plane P_(a) at a position substantially optically conjugate tomask M (an object plane of projection optical system 76) orphotosensitive substrate W (an imaging plane of projection opticalsystem 76). Reflecting elements E_(a2) and E_(b2) are arranged along asecond reference plane P_(b) at a position substantially opticallyconjugate to the pupil of projection optical system 76. Light beam 100,which may be, for example, an X-ray beam, comprises light beams 100 aand 100 b (represented by the solid lines and dotted lines,respectively) each including wavefronts 105 a and 105 b, respectively,which impinge from respective directions onto reflecting element E_(a1).Light beams 100 a and 100 b are then split into arcuate light beams 108a and 108 b, respectively, corresponding to the profile shape ofreflecting surface RS_(EA1) of reflecting element E_(a1). Arcuate lightbeams 108 a and 108 b form light source images I₁ and I₂, respectively,at respective ends of reflecting element E_(a2) in second reflectingelement group 220 b by the condensing action of reflecting surfaceRS_(EA1) of reflecting element E_(a1).

[0123] If the radiant light in light beam 100 spans the angular rangebetween light beams 100 a and 100 b and is incident reflecting elementE_(a1), a light source image is formed whose size spans light sourceimage I₁ and light source image I₂ on reflecting element E_(a2) insecond reflecting element group 220 b. Subsequently, light beams 108 aand 108 b are condensed by the reflecting and condensing action ofreflecting element E_(a2) in second reflecting element group 220 b,thereby forming light beams 310 a and 310 b which are directed towardcondenser mirror 66. Light beams 310 a and 310 b are then furthercondensed by the reflecting and condensing action of condenser mirror66, thereby forming light beams 316 a (solid lines) and 316 b (dottedlines). These beams arcuately illuminate mask M from two directions suchthat they superimpose at front side M_(F) of mask M. The optical actiondue to reflecting element E_(b1) and E_(b2) in reflecting element groups220 a and 220 b is the same as described above for reflecting elementsE_(a1) and E_(a2).

[0124] Thus, the light from plurality of light source images I (i.e.,I₁, I₂, etc.) arcuately illuminate mask M in a superimposed manner, asdescribed above. This allows for efficient and uniform illumination.Moreover, since light beams 108 a and 108 b are efficiently condenseddue to the action of each reflecting element E_(a2), E_(b2), etc., insecond reflecting element group 220 b (i.e., by the action of theseelements as field mirrors), condenser optical system 64 can be madecompact.

[0125] Since light source images I₁, I₂, etc., formed on the surface ofeach reflecting element E_(a2), E_(b2), etc., in second reflectingelement group 220 b are re-imaged at pupil position P (i.e., theentrance pupil) of projection optical system 76, Köhler illumination isachieved.

[0126] As described above in connection with the second mode forcarrying out the present invention, light having a certain dispersionangle and a particular wavelength, such as X-rays with a wavelengthλ<100 nm, is preferably employed. The mask pattern is then exposed ontowafer surface W_(S) as a photosensitive substrate with an arcuate imagefield IF′, as discussed above. The latter is efficiently formed withuniform illumination intensity while substantially maintaining theconditions of Köhler illumination, even if the illumination apparatus(elements 54-68 of exposure apparatus 200 of FIG. 13) and projectionoptical system 76 include only catoptric members.

[0127] In the second mode for carrying out the present invention, asdescribed above, reflecting elements E₁ and E₂ and condenser mirror 66are eccentric spherical surfaces. However, these surfaces can be madeaspherical surfaces, in a manner similar to that described above inconnection with the first mode for carrying out the present invention.

[0128] In the second mode for carrying out the present invention, asdescribed above, condenser optical system 64 and projection opticalsystem 76 are arranged so that optical axes A_(C) and A_(P) areorthogonal. However, with reference to FIG. 21 and exposure apparatus350, condenser optical system 64, deflecting (plane) mirror 68 andprojection optical system 76 may be arranged such that optical axesA_(C) and A_(P) are coaxial.

[0129] Next, a preferred embodiment of the second mode for carrying outthe present invention is explained with reference to FIGS. 22 and 23. Inthe present preferred embodiment, the illumination efficiency of firstand second reflecting element groups 360 a and 360 b, as describedbelow, is even greater than first and second reflecting element groups220 a and 220 b (FIGS. 14 and 15).

[0130] With reference to FIG. 22, first reflecting element group 360 ahas, along the Y-direction, three columns G_(E11)-G_(E13) of firstreflecting elements E₁ having a arcuate profile (outline) and arrangedin a row (i.e., stacked) along the Z-direction.

[0131] Reflecting element columns G_(E11)-G_(E13) each comprise aplurality of reflecting elements E_(11a)-E_(11v), E_(12a)-E_(12y), andE_(13a)-E_(13v), respectively. Each reflecting element columnsG_(E11)-G_(E13) are arranged such that certain reflecting elementstherein are each rotated by just a prescribed amount about respectiveaxes A₁-A₃ oriented parallel to the Z-axis and traversing the center oftheir respective columns.

[0132] With reference now to FIG. 23, second reflecting element group360 b includes, along the Y-direction, nine columns C1-C9 eachcomprising a plurality of second reflecting elements E₂ having a nearlyrectangular profile (outline) and arranged in a row (i.e., stacked)along the Z-direction. Second reflecting element group 360 b includes afirst subgroup G_(E21) comprising columns C1-C3, a second subgroupG_(E22) comprising columns C4-C6, and a third subgroup G_(E23)comprising columns C7-C9.

[0133] First and second reflecting element groups 360 a and 360 b areopposingly arranged, as described above in connection with apparatus 200and first and second reflecting element groups 220 a and 220 b (see,e.g., FIG. 20). Reflecting elements E_(11a)-E_(11v) of first reflectingelement column G_(E11) in first reflecting element group 360 a condenselight and form light source images I in the manner described above inconnection with first reflecting element group 220 a (see FIG. 20). Inother words, light source images I formed by reflecting elementsE_(11a)-E_(11v) are formed on the surfaces of reflecting elements E₂ infirst subgroup G_(E21). Likewise, additional light source images I arecondensed by each reflecting element E_(12a)-E_(12y) of secondreflecting element column G_(E12) in first reflecting element group 360b on the surfaces of reflecting elements E₂ in second subgroup G_(E22).Further, additional light source images I are condensed by eachreflecting element E_(13a)-E_(13v) of third reflecting element columnG_(E13) in first reflecting element group on the surfaces of reflectingelements E₂ in third subgroup G_(E23).

[0134] With reference now also to FIG. 24, reflecting elementsE_(11a)-E_(11k) in first reflecting element column G_(E11) are arrangedsuch that arbitrary reflecting elements therein are rotated by just aprescribed amount about axis A, oriented parallel to the Z-direction andtraversing the center of the first reflecting element column (centers C1_(a)-C1 _(k) of reflecting elements E_(11a)-E_(11k)).

[0135] For example, reflecting element E_(11a) is provided and fixed ina state wherein it is rotated by a prescribed amount counterclockwiseabout axis A₁. This amount of rotation is preferably very small.Reflecting element E_(11a) forms a circular-shaped light source imageI_(a) having a certain size, on the uppermost reflecting element E₂ ofcolumn C3 of first subgroup G_(E21).

[0136] Likewise, reflecting element E_(11f) is provided and fixed in astate wherein it is rotated by just a prescribed amount clockwise aboutaxis A₁. Reflecting element E_(11f) forms a circular-shaped light sourceimage I_(f) having a certain size, on the second reflecting element E₂from the top of first column C₁ of first subgroup G_(E21).

[0137] In addition, reflecting element E_(11k) is provided and fixedwithout being rotated about axis A₁. Reflecting element E_(11k) forms acircular-shaped light source image I_(k) having a certain size, on thefourth reflecting element E₂ from the top of second column C₂ of firstsubgroup G_(E21). The optical axis (not shown) of reflecting elementE_(11k) and the optical axis (not shown) of each reflecting element infirst subgroup G_(E21) are parallel to one another.

[0138] The arrangement as described above with reference to firstreflecting element column G_(E11) and first subgroup G_(E21) applies tothat between second reflecting element column G_(E12) and secondsubgroup G_(E22), and that between third reflecting element columnG_(E13) and third subgroup G_(E23), in first reflecting element group360 a.

[0139] As described above, illumination efficiency can be improved ifthe configuration of the first and second reflecting element groups 360a and 360 b (FIGS. 23 and 24) is adopted. This configuration has theadvantage that light source images I_(a), I_(f), I_(k), etc., are noteasily obscured by the profile (outline) of the second reflectingelements, as compared to the configuration of the first and secondreflecting elements in reflecting element groups 220 a and 220 b.

[0140] In the above first and second modes for carrying out the presentinvention, reflecting elements E of reflecting element group 60, andreflecting elements E₁ of reflecting element group 220 a have an arcuateprofile (outline) and having reflective surfaces RS_(E) and RS_(E1)respectively, eccentric with respect to the optical axes A_(E), andA_(E1), respectively. Consequently, constraints from the standpoint ofoptical design are significantly relaxed as compared to non-eccentricreflecting elements. This is because aberrations need only be correctedin the arcuate region at a certain image height (i.e., a certaindistance from the optical axis). Accordingly, aberrations generated bythe reflecting elements in the first reflecting element group can besufficiently controlled, resulting in very uniform arcuate illumination.

[0141] Aberrations generated by condenser optical system 64 (FIGS. 4 and13) can also be sufficiently controlled by configuring the condenseroptical system as an eccentric mirror system. This allows the aboveadvantages to be obtained synergistically. Furthermore, condenseroptical system 64 can comprise one eccentric mirror (e.g., condensermirror 66), or a plurality of such mirrors.

[0142] First and second reflecting element groups in the presentinvention may be moved by a small amount independently or as a unit in aprescribed direction (e.g., axially or orthogonal thereto).Alternatively, first and second reflecting groups may be constitutedsuch that at least one of the first reflecting element group and secondreflecting element group is capable of being inclined by a small amount.This allows for the illumination intensity distribution in the arcuateillumination field IF formed on front side M_(F) or wafer W(photosensitive substrate) to be adjusted. In addition, it is preferablethat at least one eccentric mirror in condenser optical system 64 becapable of being moved or inclined by a minute amount in a prescribeddirection (i.e., along optical axis A_(C) or orthogonal thereto).

[0143] In the present invention, it is advantageous to compactlyconfigure the exposure apparatus while simultaneously maintaining asatisfactory arcuate illumination field IF. To this end, it ispreferable in the present invention that the first reflecting elementgroup (220 a of FIG. 14 or 360 a of FIG. 22) and condenser opticalsystem 64 satisfy condition (2), discussed above.

[0144] In addition, the above modes for carrying out the presentinvention included optical integrators 56, 220, and 360 comprisingoptical elements having reflective surfaces. However, the opticalintegrators of the present invention may also comprise refractive lenselements. In this case, the cross-sectional shape of such refractivelens elements constituting a first “refractive” element group arepreferably arcuate.

[0145] Furthermore, in the present invention, first and secondreflecting element groups 220 a and 220 b and first and secondreflective element groups 360 a and 360 b are depicted as havingplurality of reflecting elements E₁ and E₂ which are densely in an arrayarranged with essentially no gaps between the individual elements.However, in the second reflective element groups 220 b and 360 b (FIG.15 and FIG. 23), plurality of reflecting elements E₂ need not be sodensely arranged. This is because numerous light source imagescorresponding respectively to the reflecting elements E₂ are formed onsecond reflective element group 220 b and 360 b, or in the vicinitythereof. Light loss does not occur to the extent that the light sourceimages fit within the effective reflecting region of each reflectingelement E₂. Accordingly, if the numerous light source images are formeddiscretely, the numerous reflecting elements E₂ in the second reflectiveelement group can be arranged discretely with gaps. The same holds truefor second reflective element group 360 b.

[0146] With reference now to FIG. 25, exposure apparatus 400 performsthe exposure operation by a step-and-scan method according to the firstmode for carrying out the present invention in a manner similar to thatdescribed in connection with exposure apparatus 50 of FIG. 4. Theelements in exposure apparatus 400 having the same function as those inexposure apparatus 50 of FIG. 4 are assigned the same reference symbol.Exposure apparatus 400 uses, in a preferred embodiment, light in thesoft X-ray region on the order of λ=5-20 nm EUV (Extreme Ultra Violet)light. In FIG. 25, the Z-direction is the direction of optical axisA_(P) of projection optical system 76 that forms a reduced image ofreflective mask M onto wafer W. The Y-direction is the direction withinthe paper surface and orthogonal to the Z-direction. The X-direction isthe direction perpendicular to the paper surface and orthogonal to theY-Z plane.

[0147] Exposure apparatus 400 projects onto wafer W the image of onepart of the circuit pattern (not shown) drawn on front side M_(F) ofmask M through projection optical system 76. The entire circuit patternof mask M is transferred onto each of a plurality of exposure regions onwafer W by scanning mask M and wafer W in a one-dimensional direction (Ydirection) relative to projection optical system 76.

[0148] Since soft X-rays (EUV light) have a low transmittance throughthe atmosphere, the optical path through which this light passes isenclosed in vacuum chamber 410 and isolated from the outside air.

[0149] With continuing reference to FIG. 25, light source 54 supplieslight beam 100 having a high illumination intensity and a wavelengthfrom the infrared region to the visible region. Light source 54 may be,for example, a YAG laser, an excimer laser or a semiconductor laser.Light beam 100 from light source 54 is condensed by condenser opticalmember 412 to a position 414. Nozzle 416 provides a jet of gaseousmatter toward position 414, where it receives laser light beam 100 of ahigh illumination intensity. At this time, the jetted matter reaches ahigh temperature due to the energy of laser light beam 100, is excitedinto a plasma state, and discharges EUV light 419 when the gaseousmatter transitions to a low-energy state.

[0150] An elliptical mirror 418 is arranged at the periphery of position414 such that its first focal point (not shown) nearly coincides withconvergent position 414. A multilayer film is provided on the innersurface 418S of elliptical mirror 418 to reflect EUV light 419. Thereflected EUV light 419 is condensed at a second focal point 420 ofelliptical mirror 418 and then proceeds to a collimating mirror 422,which is preferably concave and may be paraboloidal. Collimating mirror422 is positioned such that the focal point (not shown) thereof nearlycoincides with second focal point 420 of elliptical mirror 418. Amultilayer film is provided on the inner surface 422S of collimatingmirror 422 to reflect EUV light 419. Condenser optical member 412,elliptical mirror 418 and collimating mirror 422 constitute a condenseroptical system. Light source 54, and the condenser optical systemconstitute a light source unit LSU with optical axes A_(L1) and A_(L2).EUV light 419 reflected by collimating mirror 422 proceeds to opticalintegrator (e.g. reflecting type fly's eye system) 220 in a nearlycollimated state. A multilayer film is provided onto the plurality ofreflecting surfaces constituting first and second reflecting elementgroups 220 a and 220 b to enhance reflection of EUV light 419.

[0151] Exposure apparatus 400 further includes a first variable aperturestop AS1 provided at the position of the reflecting surface of secondreflecting element group 220 b or in the vicinity thereof. Variableaperture stop AS1 is capable of varying the numerical aperture NA of thelight illuminating mask M (i.e., the illumination numerical aperture).First variable aperture stop AS1 has a nearly circular variableaperture, the size of which is varied by a first drive system DR1operatively connected thereto.

[0152] A collimated EUV light beam 428 from collimating mirror 422includes a wavefront 430 that is split by first reflecting element group220 a and is condensed to form a plurality of light source images (notshown), as discussed above. The plurality of reflecting elements E₂ ofsecond reflecting element group 220 b are positioned in the vicinity ofthe location of the plurality of light source images. The plurality ofreflecting elements E₂ of second reflecting element group 220 bsubstantially acts as field mirrors. In this manner, optical integrator220 forms a plurality of light source images as secondary light sourcesfrom approximately parallel light beam 428. The EUV lightbeam 432(comprising a plurality of light beams) from the secondary light sourcesformed by optical integrator 220 proceeds to condenser mirror 66positioned such that the secondary light source images are formed at ornear the focal point of the condenser mirror. Light beam 432 isreflected and condensed by condenser mirror 66, and is deflected to maskM by fold mirror 68. A multilayer film that reflects EUV light isprovided on surface 66S of condenser mirror 66 and surface 68S of foldmirror 68. Condenser mirror 66 condenses EUV light in light beam 432 ina superimposed manner, forming an arcuate illumination field on frontside M_(F) of mask M.

[0153] A multilayer film that reflects EUV light is provided on frontside M_(F) of mask M. Thus, EUV light incident thereon is reflected frommask M as light beam 434. The latter passes to projection system 76,which images mask M onto wafer W as the photosensitive substrate.

[0154] In the present mode for carrying out the present invention, it ispreferable to spatially separate the optical paths of light beam 432that proceeds to mask M and light beam 434 reflected by the mask thatproceeds to projection optical system 76. In this case, the illuminationsystem is nontelecentric, and projection optical system 76 is alsonontelecentric on the mask M side. Projection optical system 76 alsoincludes multilayer films that reflects EUV light provided on thereflecting surfaces of the four mirrors 78 a-78 d for enhancing EUVlight reflectivity.

[0155] Mirror 78 c in projection optical system 76 is arranged at thepupil position or in the vicinity thereof. A second variable aperturestop AS2 capable of varying the numerical aperture of projection opticalsystem 76 is provided at the reflecting surface of mirror 78C or in thevicinity thereof. Second variable aperture stop AS2 has a nearlycircular variable aperture, the diameter of which is capable of beingvaried by second drive system DR2 operatively connected thereto.

[0156] The ratio of the numerical aperture of the illumination systemNA_(I) to the numerical aperture NA_(P) of projection optical system 76is called the coherence factor, or σ value (i.e., σ=NA_(I)/NA_(P)).

[0157] Due to the degree of fineness of the pattern on mask M to betransferred to wafer W and the process of transferring this pattern towafer W, it is often necessary to adjust the resolving power and depthof focus and the like of projection optical system 76 by varying the σvalue. Consequently, exposure information related to the exposureconditions of each wafer W sequentially mounted on wafer stage WS by atransport apparatus (not shown) (wafer transport map and the like thatincludes exposure information), and the mounting information of eachtype of mask M sequentially mounted on mask stage MS is input to acontrol apparatus MCU through input apparatus IU, such as a consoleelectrically connected thereto. Control apparatus MCU is electricallyconnected to first and second drive systems DR1 and DR2. Based on theinput information from input apparatus IU, each time a wafer W ismounted on substrate stage WS, control apparatus MCU determines whetherto change the σ value. If control apparatus MCU determines that it isnecessary to change the σ value, a signal is sent therefrom to at leastone of two drive systems DR1 and DR2, to vary at least one aperturediameter among first variable aperture stop AS1 and second variableaperture stop AS2. Consequently, the appropriate exposure can beachieved under various exposure conditions. The light intensitydistribution at a pupil position of projection optical system 76 ischanged by using the illumination condition changing system includingfirst variable aperture stop AS1, second variable aperture stop AS2 anddrive systems DR1 and DR2.

[0158] With continuing reference to FIG. 25, it is preferable in thepresent embodiment to replace collimating mirror 422 with a collimatingmirror having a different focal length, in response to varying theaperture diameter of first variable aperture stop AS1. As a result, thediameter of EUV light beam 428 incident optical integrator 220 can bechanged in accordance with the size of the opening of first variableaperture stop AS1. In this manner, illumination at an appropriate σvalue is enabled while maintaining a high illumination efficiency.

[0159] The light illumination intensity distribution on mask M or waferW of exposure apparatus 400 may be nonuniform, in the sense that it isbiased. In this case, this bias can be corrected by making light beam428 eccentric prior to traversing reflecting element group 220 a. Forexample, by making collimating mirror 422 slightly eccentric, the biasof the light illumination intensity distribution can be corrected. Inother words, if the bias of the intensity distribution occurs in thelateral X-direction of the arcuate illumination field IF (or in arcuateimage field IF′ on surface W_(S) of wafer W), the bias can be correctedby moving collimating mirror 422 in the X-direction. If the illuminationintensity in arcuate illumination field IF at the center part andperipheral part differs in the width direction, respectively, the biasof the light illumination intensity distribution can be corrected bymoving collimating mirror 422 in the same direction.

[0160] When varying at least one aperture diameter among first variableaperture stop AS1 and second variable aperture stop AS2, there are caseswherein the illumination deteriorates. For example, illuminationnon-uniformity occurs over the arcuate illumination field IF. In thiscase, it is preferable to correct illumination non-uniformity and thelike over the arcuate illumination field IF by slightly moving at leastone of collimating mirror 422, optical integrator 220 and condensermirror 66.

[0161] With reference now to FIG. 26, exposure apparatus 450, which isan alternate embodiment of exposure apparatus 400, is now described byhighlighting the difference between these two apparatus.

[0162] The first difference between exposure apparatus 400 and exposureapparatus 450 is that exposure apparatus includes a turret plate 452instead of first variable aperture stop AS1. Turret plate 452 isconnected to a drive shaft 454, connected to first drive system DR1.Turret plate 452 is thus rotatable about a rotational axis A_(R) byfirst drive system DR1. With reference to FIG. 27, turret plate 452comprises a plurality of aperture stops 456 a-456 f having differentshapes and sizes. Turret plate 452 is discussed in more detail, below.

[0163] With reference again to FIG. 26, exposure apparatus 450 furtherincludes an adjustable annular light beam converting unit 460. Thelatter converts EUV light beam 428 having a circular cross-section to alight beam 428′ having an annular (ring-shaped) light beam crosssection. Unit 460 is movably provided in the optical path (e.g., lightbeam 428) between collimating mirror 422 and first reflecting elementgroup 220 a of optical integrator 220.

[0164] Annular light beam converting unit 460 has a first reflectingmember 460 a with a ring-shaped reflecting surface and second reflectingmember 460 b having a conical reflecting surface. To vary the ratio ofthe inner diameter of the ring to the outer diameter of (the so-called“annular ratio”) of light beam 428′, first reflecting member 460 a andsecond reflecting member 460 b are moved relative to one another.

[0165] The insertion and removal of annular light beam converting unit460 in and out of light beam 428 and the relative movement of firstreflecting member 460 a and second reflecting member 460 b is performedby a third drive system DR3 in operable communication with annular lightbeam converting unit 460 and electrically connected to control apparatusMCU.

[0166] With reference now again to FIG. 27, further details concerningturret plate 452 and annular light beam converting unit 460 areexplained. Turret plate 452, as discussed briefly above, includes aplurality of different aperture stops 456 a-456 f and is rotatable aboutaxis A_(R). Aperture stop 456 a has an annular (donut-shaped) aperture,and aperture stops 456 b and 456 e have circular openings with differentaperture diameters. Aperture stop 456 c has four fan-shaped openings,and aperture stop 456 d has four circular openings. Aperture stop 456 fhas an annular ratio (ratio of outer diameter r_(fo) to inner diameterr_(fi) of opening 456 _(fo) of the annular shape) different from that ofaperture stop 456 a (with outer diameter r_(ao) and inner diameterr_(ai)).

[0167] In exposure apparatus 450, input apparatus IU is for inputtinginformation necessary for selecting the method of illuminating mask Mand exposing wafer W. For example, input apparatus IU inputs exposureinformation related to the exposure conditions of each wafer Wsequentially mounted by an unillustrated transport apparatus (wafertransfer map and the like that includes the exposure information), andmounting information of each type of mask M sequentially mounted on maskstage MS. This information is based on the degree of fineness of themask pattern to be transferred to wafer W and the process associatedwith transferring the pattern to wafer W.

[0168] For example, control apparatus MCU can select illumination statessuch as “first annular illumination,” “second annular illumination,”“first normal illumination,” “second normal illumination,” “firstspecial oblique illumination,” and “second special obliqueillumination,” based on the information input into input apparatus IU.

[0169] “Annular illumination” aims to improve the resolving power anddepth of focus of projection optical system 76. It does so byilluminating EUV light onto mask M and wafer W from an oblique directionby setting the shape of the secondary light sources formed by opticalintegrator 220 to an annular shape. “Special oblique illumination” aimsto further improve the resolving power and depth of focus of projectionoptical system 76. It does so by illuminating EUV light onto catoptricmask M and wafer W by making the secondary light sources formed byoptical integrator 220 a discrete plurality of eccentric light sources.These light sources are made eccentric by just a predetermined distancefrom the center thereof. “Normal illumination” is one that aims toilluminate mask M and wafer W based on an optimal σ value by making theshape of the secondary light sources formed by optical integrator 220nearly circular.

[0170] Based on the input information from input apparatus IU, controlapparatus MCU controls first drive system DR1 to rotate turret plate452, second drive system DR2 to change the aperture diameter of aperturestop AS2 of projection optical system 76, and third drive system DR3 toinsert and remove annular light beam converting unit 460 in and outlight beam 428. Control apparatus MCU changes the relative spacingbetween the two reflecting members 460 a and 460 b in annular light beamconverting unit 460.

[0171] If the illumination state on mask M is set to normalillumination, control apparatus MCU selects “first normal illumination”or “second normal illumination,” based on the input information frominput apparatus IU. “First normal illumination” and “second normalillumination” have different σ values.

[0172] For example, if control apparatus MCU selects “first normalillumination,” control apparatus MCU rotates turret plate 452 by drivingfirst drive system DR1 so that aperture stop 456 e is positioned at thesecondary light sources formed on exit side 220 be of second reflectiveelement group 220 b. Simultaneously, control apparatus MCU changes, asneeded, the aperture diameter of second aperture stop AS2 via seconddrive system DR2. At this point, if annular light beam converting unit460 is set in light beam 428, control apparatus MCU withdraws this unitfrom the illumination optical path via third drive system DR3.

[0173] If EUV light illuminates the mask pattern of mask M based on theset condition of the illumination system mentioned above, the patterncan be exposed onto wafer W through projection optical system 76 basedon the appropriate “first normal illumination” condition (i.e., anappropriate σ value).

[0174] If control apparatus MCU selects “second normal illumination,”control apparatus MCU rotates turret plate 452 by driving first drivesystem DR1 so that aperture stop 456 b is positioned at the secondarylight sources formed on exit side 220 be of second reflective elementgroup 220 b. Simultaneously, control apparatus MCU changes, as needed,the aperture diameter of the second aperture stop AS2 via second drivesystem DR2. At this point, if annular light beam converting unit 460 isset in light beam 428, control apparatus MCU withdraws this unit fromthe illumination optical path via third drive system DR3.

[0175] If EUV light illuminates the mask pattern of mask M based on theset condition of the illumination system mentioned above, the patterncan be exposed onto wafer W through projection optical system 76 basedon the appropriate “second normal illumination” condition (i.e., σ valuelarger than that of first normal illumination).

[0176] As mentioned in connection with exposure apparatus 400 (FIG. 25),it is preferable in exposure apparatus 450 (FIG. 26) to replacereflecting mirror 422 with a reflecting mirror having a focal lengthdifferent therefrom in response to the varying of the aperture diameterof first variable aperture stop AS1. As a result, the beam diameter oflight beam 428 can be changed in response to the size of the opening offirst variable aperture stop AS1. Thus, illumination is enabled with anappropriate σ value while maintaining a high illumination efficiency.

[0177] If the illumination with respect to mask M is set to obliqueillumination, control apparatus MCU selects, based on the inputinformation from input apparatus IU, one among “first annularillumination,” “second annular illumination,” “first special obliqueillumination” and “second special oblique illumination.” “First annularillumination” and “second annular illumination” differ in that theannular ratios of the secondary light sources formed annularly aredifferent. “First special oblique illumination” and “second specialoblique illumination” differ in their secondary light sourcedistributions. In other words, the secondary light source in “firstspecial oblique illumination” is distributed in four fan-shaped regions(aperture stop 456 c), and the secondary light sources in “secondspecial oblique illumination” are distributed in four circular regions(aperture stop 456 d).

[0178] If “first annular illumination” is selected, control apparatusMCU rotates turret plate 452 by driving drive system DR1 so thataperture stop 456 a is positioned at the position of the secondary lightsources formed on exit side 220 be of second reflective element group220 b. If “second annular illumination” is selected, control apparatusMCU rotates turret plate 452 by driving drive system DR1 so thataperture stop 456 f is positioned at the position of the secondary lightsources formed on exit side 220 be of second reflective element group220 b. If “first special oblique illumination” is selected, controlapparatus MCU rotates turret plate 452 by driving drive system DR1 sothat aperture stop 456 c is positioned at the position of the secondarylight sources formed on exit side 220 be of second reflective elementgroup 220 b. If “second special oblique illumination” is selected,control apparatus MCU rotates turret plate 452 by driving drive systemDR1 so that aperture stop 456 d is positioned at the position of thesecondary light sources formed on exit side 220 be of second reflectiveelement group 220 b.

[0179] If one among the above four aperture stops 456 a, 456 c, 456 d,and 456 f is set in light beam 428, control apparatus MCU simultaneouslychanges, as needed, the aperture diameter of second aperture stop AS2 inprojection optical system 76 via second drive system DR2.

[0180] Next, control apparatus MCU sets annular light beam convertingunit 460 in light beam 428 via third drive system DR3 and adjusts theunit. The operation of setting and adjusting annular light beamconverting unit 460 is performed as described below.

[0181] First, if annular light beam converting unit 460 is not set inlight beam 428, control apparatus MCU sets the unit in the light beamvia third drive system DR3.

[0182] Next, control apparatus MCU changes the relative spacing of thetwo reflecting members 460 a and 460 b in annular light beam convertingunit 460 via third drive system DR3 so that the annular light beam (nowlight beam 428′) is efficiently guided to the opening of one aperturestop among the four aperture stops 456 a, 456 c, 456 d, and 456 f set onexit side 220 be of second reflective element group 220 b. As a result,annular light beam converting unit 460 can convert light beam 428incident thereon to annular light beam 428′ having an appropriateannular ratio.

[0183] Secondary light sources (not shown) formed by optical integrator220 can, by the setting and adjustment of the above annular light beamconverting unit 460, be rendered annular secondary light sources havingan appropriate annular ratio corresponding to the opening of each of thefour aperture stops 456 a, 456 c, 456 d, and 456 f. Thus, obliqueillumination of mask M and wafer W can be performed with a highillumination efficiency. The light intensity distribution at a pupilposition of projection system 76 is changed by using the illuminationcondition changing system including turret plate 452 having plurality ofaperture stops 456 a-456 f, second variable aperture stop AS2, annularlight beam converting unit 460 and three drive systems DR1, DR2 and DR3.

[0184] Thus, one of a plurality of aperture stops 456 a-456 f havingmutually differing shapes and sizes can be set in the illuminationoptical path by rotating turret plate 452. Thus, the illumination state,such as illumination unevenness, of the arcuate illumination field IF orthe arcuate image field IF′ may change. It is preferable to correct thisillumination unevenness by slightly moving at least one of collimatingmirror 422, optical integrator 220 and condenser mirror 66.

[0185] With continuing reference to FIG. 26 and exposure apparatus 450,information like the illumination condition is input to controlapparatus MCU via input apparatus IU. However, a detector (not shown)that reads the information on mask M may also be provided. Informationrelated to the illumination method is recorded by, for example, abarcode and the like at a position outside the region of the maskpattern of mask M. The detector reads the information related to thisillumination condition and transmits it to control apparatus MCU. Thelatter, based on the information related to the illumination condition,controls the three drive apparatus DR1-DR3, as described above, to setthe illumination.

[0186] In exposure apparatus 450, one of aperture stops 456 a-456 f isprovided at exit side 220 be of optical element group 220 b (i.e., theposition of the secondary light sources). However, illumination byaperture stops 456 c and 456 d having four eccentric openings need notbe provided. Also, aperture stops 456 a-456 f formed on turret plate 452are not essential to the present invention in the case of performing“annular illumination” or “normal illumination,” as will be understoodby one skilled in the art from the theory of the present invention.

[0187] Four eccentric light beams can be formed by constituting firstreflecting member 460 a, in annular light beam converting unit 460, bytwo pairs of plane mirror elements (not shown) arranged opposite oneanother and mutually inclined, and by constituting the reflectingsurface of reflecting member 460 a in a square column shape. As aresult, the secondary light sources formed by optical integrator 220 canbe rendered quadrupole secondary light sources eccentric to the centerthereof. Accordingly, EUV light corresponding to the openings ofaperture stops 456 c and 456 d having four eccentric openings can beformed.

[0188] With reference now to FIG. 28, exposure apparatus 500, which isanother modified version of exposure apparatus 400, is now described. Inexposure apparatus 500, as well as in exposure apparatus 550 and 600discussed below (FIGS. 29 and 30), elements AS1, 452, AS2, DR1, DR2, IUand MCU are included, as discussed above. However, these elements arenot shown in FIGS. 28-36 for the sake of illustration.

[0189] The difference between exposure apparatus 400 shown and exposureapparatus 500 of FIG. 28 is that the latter includes an auxiliaryoptical integrator 510. With reference also to FIGS. 29 and 30,auxiliary optical integrator 510 includes a first auxiliary reflectingelement group 510 a and a second auxiliary reflecting element group 510b. Exposure apparatus 500 further includes a relay mirror 514 as a relayoptical system. Optical integrator 510 and mirror 514 are respectivelyarranged in the optical path between reflecting mirror 422 and opticalintegrator 220. Auxiliary optical integrator 510 is preferably acatoptric fly's eye system. If viewed in order from light source 54,auxiliary optical integrator 510 can be seen as a first opticalintegrator (i.e., first multiple light source forming optical system),and in combination with a second or main optical integrator 220.

[0190] First auxiliary reflecting element group 510 a comprises aplurality of reflecting elements E_(510a) (FIG. 29) arranged on theentrance side 510 ae of auxiliary optical integrator 120. ElementsE_(510a) are preferably formed in a shape similar to the overall shape(outline) of first reflecting element group 220 a arranged on theentrance side of optical integrator 220 (see FIGS. 14 and 22). However,if reflecting elements E_(510a) are constituted in a shape as shown inFIGS. 14 and 22, it is difficult to densely arrange the reflectingelements without gaps in between. Consequently, with reference to FIGS.29 and 30, each of the reflecting elements E_(510a) in first auxiliaryreflecting element group 510 a is nearly square in shape. Now, the crosssection of light beam 428 incident first auxiliary reflecting elementgroup 510 a is nearly circular, and reflecting elements E_(510a) arearranged in a row so that the overall shape (outline) of this group isnearly circular. As a result, first auxiliary reflecting element group510 a can form numerous light source images (secondary light sources)with high illumination efficiency at the position of second auxiliaryreflecting element group 510 b, or in the vicinity thereof.

[0191] The overall shape (outline) of second auxiliary reflectingelement group 510 b arranged on the exit side of auxiliary opticalintegrator 510 is preferably formed in a similar shape to that ofreflecting elements E₂ comprising second reflecting element group 220 barranged on the exit side of optical integrator 220, as shown in FIGS.15 and 23. Each reflecting element E_(510b) in second auxiliaryreflecting element group 510 b is preferably shaped similar to the shapeof the light source images formed by reflecting elements E_(510a) infirst auxiliary reflecting element group 510 a so that it receives allthe light source images.

[0192] In exposure apparatus 500, main optical integrator 220 preferablycomprises first and second reflecting element groups 360 a and 360 b(FIGS. 22 and 23) in place of reflecting element groups 220 a and 220 b(both reference numbers being used hereinafter to indicate either can beused for the first and second reflecting element groups of main opticalintegrator 220). Consequently, plurality of reflecting elements E₂ insecond reflecting element group 360 b (220 b) arranged on the exit sideof optical integrator 220 have a shape that is nearly square, as shownin FIG. 23.

[0193] With continuing reference to FIG. 28, the light source images(not shown) formed by each of the plurality of reflecting elementsE_(510a) comprising first auxiliary reflecting element group 510 a inauxiliary optical integrator 510 are nearly circular. Thus, the shape ofeach reflecting element E_(510b) of second auxiliary reflecting elementgroup 510 b is nearly square, as shown in FIG. 30. In addition, sincethe shape of each reflecting element E₂ that comprises second reflectingelement group 360 b (220 b) arranged on the exit side of main opticalintegrator 220 is nearly square, the reflecting elements therein arearranged in rows so that the overall shape (outline) of second auxiliaryreflecting element group 510 b is nearly square, as shown in FIG. 30.

[0194] In this manner, in exposure apparatus 500 of FIG. 28, first andsecond auxiliary reflecting element groups 510 a and 510 b arepreferably constituted by the same type of reflecting element group.This allows manufacturing costs to be controlled.

[0195] It is also preferable that second reflecting element group 220 band condenser mirror 66 satisfy the relation in condition (2), discussedabove.

[0196] With continuing reference to FIG. 28, the action of opticalintegrators 220 and 510 are now explained in more detail. By thearrangement of optical integrators 220 and 510, a plurality of lightsource images (not shown) are formed. The number of light source imagescorresponds to the product of the number (N) of reflecting elements inone of the reflecting element groups in optical integrator 510 and thenumber (M) of reflecting elements in one of the reflecting elementgroups in main optical integrator 220. The plurality of light sourceimages are formed on the surface of one of the second reflecting elementgroups 360 b (220 b) in main optical integrator 220, or in the vicinitythereof. Accordingly, many more light source images (tertiary lightsources, not shown) than the light source images (secondary lightsources) formed by auxiliary optical integrator 510 are formed on thesurface of main reflecting element group 360 b (220 b), or in thevicinity thereof. Light from the tertiary light sources from mainoptical integrator 220 arcuately illuminate mask M in a superimposedmanner. Thus, the illumination distribution in arcuate illuminationfield IF formed on mask M and arcuate image field IF′ formed on wafer Wcan be rendered more uniform, allowing for a much more stable exposure.

[0197] Relay mirror 514 arranged between optical integrators 510 and 220condenses light beam 520 from the numerous light source images(secondary light sources) from optical integrator 510, thereby forming alight beam 522 directed to optical integrator 220. Relay mirror 514serves the function of making the near surface (i.e., entrance side 510ae) of reflecting element group 510 a and the near surface (i.e.,entrance side 220 ae) of the reflecting element group 220 a (360 a)optically conjugate. Relay mirror 514 also serves the function of makingthe near surface (i.e., exit side 510 be) of reflecting element group510 b and the near surface (i.e., exit side 220 be) of the reflectingelement group 360 b (220 b) optically conjugate. Surface 510 ae andsurface 220 ae are optically conjugate mask M and wafer W. Also, surface220 be and surface 510 be are optically conjugate the pupil ofprojection optical system 76 and the position of aperture stop AS2.

[0198] With continuing reference to FIG. 28 and exposure apparatus 500,if the illumination intensity distribution in arcuate illumination fieldIF is biased, it is preferable to move auxiliary optical integrator 510(i.e., move reflecting element groups 510 a and 510 b as a unit). Ifreflecting element groups 360 a (220 a) and 360 b (220 b) in mainoptical integrator 220 are made eccentric in the X-direction orZ-direction, the biased component of the illumination intensitydistribution can be corrected and a uniform illumination intensitydistribution can be obtained by the action of coma generated by mainoptical integrator 220.

[0199] For example, if bias occurs in the illumination intensitydistribution in the lateral direction (X-direction) of arcuateillumination field IF or in arcuate image field IF′, respectively, thebias can be corrected by moving optical integrator 510 in theX-direction. In addition, if the illumination intensity differs betweenthe center part and peripheral part in the width direction of thearcuate illumination field IF or arcuate image field IF′, the bias inthe illumination intensity distribution can be corrected by movingauxiliary optical integrator 510 in the same direction.

[0200] For exposure apparatus 500 to properly form an image of mask M onwafer W, it is preferable to form a well-corrected image of the exitpupil of the illumination system at the center of the entrance pupil ofprojection optical system 76 (i.e., an image of tertiary light sourcesformed by optical integrator 220). If this condition is not satisfied,it is preferable to move the position of the exit pupil of theillumination system, to adjust the telecentricity of the illuminationsystem, and to coordinate with the position of the entrance pupil ofprojection optical system 76. For example, by moving main opticalintegrator 220 (i.e., two reflecting element groups 360 a (220 a) and360 b (220 b)) and first aperture stop AS1 as a unit, the telecentricityof the illumination system is adjusted, and the center of the exit pupilimage of the illumination system is made to coincide with the center ofthe entrance pupil of projection optical system 76. However, if it isnot necessary to provide aperture stop AS1 at the position of thetertiary light sources, then reflecting element groups 360 a (220 a) and360 b (220 b) in main optical integrator 220 are preferably moved as aunit.

[0201] In exposure apparatus 400 (FIG. 25) and exposure apparatus 450(FIG. 26), discussed above, to match the image of the exit pupil of theillumination system to the center of the entrance pupil of projectionoptical system 76, the center of the exit pupil image of theillumination system can be made to coincide with the center of theentrance pupil of projection optical system 76 by moving opticalintegrator 220 and first aperture stop AS1 as a unit. If it is notnecessary to provide aperture stop AS1 at the position of the secondarylight sources, then reflecting element groups 360 a (220 a) and 360 b(220 b) are preferably moved as a unit.

[0202] In exposure apparatus 400 (FIG. 25), 450 (FIG. 26) and 500 (FIG.28), discussed above, light source unit LSU in practice generallyoccupies a considerable volume. It is a possibility that this volume canbecome equal to or larger than the exposure apparatus body unit (opticalsystem and control system from optical integrator 220 to wafer stageWS). Consequently, it may be preferred to separate light source unit LSUand the exposure apparatus body unit, with light source unit LSU and theexposure apparatus body unit installed independently on a base. In thiscase, strain in the floor may occur due to, for example, vibration ofthe floor caused by people near the apparatus, or due to the weight ofthe light source unit and the exposure apparatus body unit themselves.Thus, there is a risk that the light source unit optical axes (A_(L1)and A_(L2)) and the optical system axis (e.g., axis A_(P) or A_(C)) inthe exposure apparatus body unit will become displaced, upsetting theadjustment state of the exposure apparatus.

[0203] Accordingly, with reference to FIG. 28, it is preferable toarrange a photoelectric detector 528 in the optical path of the exposureapparatus body unit (i.e., in the optical path from optical integrator220 to wafer stage WS). Photodetector 528 photoelectrically detects arelative displacement of light source unit optical axis A_(L1) and/orA_(L2), and provides a control signal to a detector control unit 530that is operably connected to and controls the inclination ofcollimating mirror 422. Consequently, even if vibration of the floor dueto walking and the like of operators or strain in the floor occurs, atleast one of light source unit optical axes A_(L1) and A_(L2) and anoptical axis (e.g., optical axis A_(p) or A_(c)) of the optical systeminside the exposure apparatus body unit can be aligned automatically.

[0204] Because it is difficult to obtain high reflectance for soft X-raymirrors, it is desirable to reduce the number of mirrors in the opticalsystem of a soft X-ray exposure apparatus. One technique to reduce thenumber of mirrors in the present invention involves eliminatingcondenser mirror 66. This is achieved by bending the entirety of one ofsecond reflecting element group 360 b (220 b) in optical integrator 220(FIG. 15 and FIG. 23). In other words, by constituting second reflectingelement group 360 b (220 b) by arranging in a row numerous reflectingelements E₂ within a reference spherical surface (reference curvedsurface) having a predetermined curvature, the function of condensermirror 66 can be incorporated into second reflecting element group 360 b(220 b). Thus, with reference now to FIG. 31, and exposure apparatus 550and also to FIG. 21, a second reflective element group 220 c combinesthe function of condenser mirror 66 in one of second reflecting elementgroup 360 b (220 b) in optical integrator 220. By modifying theconfiguration of second reflecting element group 360 b (220 b) of mainoptical integrator 220 of exposure apparatus 500 (FIG. 28), the functionof condenser mirror 66 can be combined therein as well. Projectionoptical system 76 in FIG. 31 comprises six mirrors 78 a-78 f to stillfurther improve imaging performance.

[0205] Exposure apparatus 400 to 550 of the present invention preferablyuse a laser plasma light source. However, such a light source has thedisadvantage of generating a spray of microscopic matter. If opticalparts are contaminated by this fine spray, the performance of theoptical system, which is based in part on mirror reflectance andreflection uniformity, deteriorates. Thus, with reference to FIG. 32 andexposure apparatus 600, it is preferable to arrange, with vacuum chamber410, a sub-chamber 602 which houses a portion of nozzle 416, andelliptical mirror 418. Chamber 602 includes a filter window 604 capableof transmitting only soft X-rays while blocking transmission of thedispersed microscopic particles. A thin film of a light element (i.e., amembrane) may be used as filter 604. In the present arrangement, vacuumchamber 410 also includes a second window 606 capable of passing lightfrom light source 54 into chamber 602. This arrangement may be used withany of exposure apparatus 400-550 of the present invention as well.

[0206] If filter 604 is provided between elliptical mirror 418 andcollimator collimating mirror 422, operating costs can be kept low byreplacing elliptical mirror 418 and filter 604 when contaminationoccurs.

[0207] Exposure apparatus 400-600 are enclosed in vacuum chamber 410,since the transmittance of soft X-rays through the atmosphere isrelatively low. Nevertheless, it is difficult for the heat remaining inthe optical parts to escape. As a result, the mirror surfaces tend towarp. Accordingly, it is preferable to provide a cooling mechanism (notshown) for each of the optical parts inside vacuum chamber 410. Morepreferably, if a plurality of cooling mechanisms is attached to eachmirror and the temperature distribution inside the mirror controlled,then warping of the mirrors during the exposure operation can be furthercontrolled.

[0208] In addition, a multilayer film is provided on the reflectingsurfaces in exposure apparatus 400-600. It is preferable that thismultilayer film be formed by layering a plurality of materials fromamong molybdenum, lithium, rhodium, silicon and silicon oxide.

[0209] As is apparent from the above description, the present inventionhas many advantages. A first advantage of the present invention is thata surface of an object, such as a mask surface, can be illuminateduniformly and efficiently over an arcuately shaped illumination fieldwhile maintaining a nearly fixed numerical aperture of the illuminationlight. A second advantage is that the illumination coherence can bevaried to suit the particular pattern on the mask to be imaged onto thewafer by varying the size of the aperture stops in the illuminator andin the projection optical system. A third advantage is that theillumination beam can be altered through the use of an adjustableannular light beam converting unit. A fourth advantage is that one of aplurality of aperture stops can be inserted into the illumination systemto alter the illumination coherence. A fifth advantage is that a bias inthe illumination uniformity can be compensated by measuring the lightbeam uniformity and adjusting the collimating mirror in the illuminatorbased on the uniformity measurement.

[0210] While the present invention has been described in connection withpreferred embodiments, it will be understood that it is not so limited.On the contrary, it is intended to cover all alternatives, modificationsand equivalents as may be included within the spirit and scope of theinvention as defined in the appended claims.

What is claimed is:
 1. An exposure apparatus for exposing an image of apattern of a mask onto a photosensitive substrate with EUV radiation,comprising: a radiation source unit; and an exposure apparatus body unitthat comprises: an optical integrator; a mirror arranged in an opticalpath between the radiation source unit and the optical integrator; adetector arranged in an optical path of the exposure apparatus bodyunit; and a controller which is connected to the detector and whichcontrols an inclination of the mirror based on an output from thedetector; and wherein the radiation source unit and the exposureapparatus body unit are installed independently.